"They are not effective for low back pain and radiating leg pain, and they are associated with increased risk of side effects," said senior researcher Christine Lin. She's an associate professor with the University of Sydney School of Public Health, in Australia.

Physicians mindful of the opioid crisis have been desperately searching for new painkillers that could either replace narcotics like OxyContin or reduce the need for them, said Dr. Charla Fischer, a spine surgeon with NYU Langone Health in New York City.

"There's a huge push to find treatments for back pain other than narcotics, and even other than anti-inflammatories because there's always the risk of side effects, like ulcers," Fischer said.

Much interest has focused on drugs normally used to curb epileptic seizures, Fischer noted. These anticonvulsants have been shown to ease nerve pain in diabetics, so doctors thought they might also be useful in treating back pain.

As a result, anticonvulsant prescriptions aimed at treating back and neck pain have skyrocketed in the United States, Lin said.

The drug gabapentin (Neurontin) was the 10th most commonly prescribed medication in the United States in 2016, she noted. About 64 million prescriptions were dispensed, up from 39 million in 2012.

According to Fischer, researchers are still considering anticonvulsants for other uses involving spine pain.

Some studies have shown that a cocktail of anticonvulsants and NSAIDs before surgery can reduce the amount of narcotics patients need afterward, Fischer said.

"From that perspective, there still might be a role for these medications in spine surgery. But for chronic back and leg pain there have been multiple studies that really don't show this effect has borne out as we had hoped," Fischer said.

The new study was published July 3 in the CMAJ (Canadian Medical Association Journal).